Production of ultrashort electron bunches is needed in a number of applications, ranging from time-resolved electron microscopy to free-electron laser injection.
An ultrashort electron beam can be generated by many methods, including for example direct field vacuum acceleration, Wakefield acceleration and high power longitudinal field acceleration.
Theoretical studies on high power longitudinal field acceleration suggest using a radially polarized laser beam from an extremely high power laser system, i.e. in the Petawatt range. The power threshold for acceleration is related to the following equation, in Terawatts (TW), where e and me are respectively the electron charge and mass, η0 is the impedance of free space, λ0 is the central laser wavelength, ω0 is central laser frequency:
      P    seuil    =                              π          5                          2          ⁢                      η            0                              ⁢                        (                                    ω              0                                      λ              0                                )                4            ⁢                        (                                                    m                e                            ⁢                              c                2                                      e                    )                2              ≃                  1        10            ⁢                        (                                    ω              0                                      λ              0                                )                4            ⁢      T      ⁢                          ⁢              W        .            
Such method uses a long focal length configuration, i.e. low numerical aperture (NA), and requires high power systems (Petawatt level systems). Moreover, it requires a carrier envelope phase (CEP) stable laser pulse for stable electron beam. Stable CEP Petawatt laser systems are not currently available.
There is still a need in the art for an all-optical method and system for generating ultrashort charged particle beam.